Tara is the female Buddha of enlightened activity, of which there are 4 types: pacifying, increasing, overpowering and wrathful. Each of these is represented by a different colour:
White represents the enlightened activity of pacifying, for example overcoming sickness, causes of untimely death and obstacles to success in one’s life or one’s practice.
Yellow represents the enlightened activity of increasing the positive qualities conducive to a long life, peace, happiness and success in one’s Dharma practice.
Red represents the enlightened activity of power, or overpowering external forces that cannot be tamed through the first two activities, for example, removing obstacles to sickness, untimely death, etc., and forcefully accumulating conducive conditions for one’s Dharma practice.
Black represents the enlightened activity of wrath, which involves using forceful methods for accomplishing activities for enlightened purposes that cannot be accomplished through other means.